A large number of plastic containers that are now used, for example, plastic bottles and the like, are produced using a stretch blow-molding method. In the stretch blow-molding method, a so-called preform, which can have a tubelike shape, has a bottom on its one longitudinal end and a neck area with formed threaded sections or the like on its other longitudinal end, is inserted into a mold cavity of a blow mold, and is inflated by a medium that is injected with overpressure. Here, the preform is additionally stretched in the axial direction with a stretching mandrel that is inserted through the neck opening. After this blow-molding and stretching process, the finished, stretch-hardened plastic container is demolded, or removed, from the blow mold.
A raw material that has been used for the production of plastic containers in the stretch blow-molding method is polyethylene terephthalate (PET). As a result of the extensive stretching done in the stretch blow-molding method, PET has very good mechanical strength values. For example, in the stretch blow-molding method of PET, a total stretching factor of up to 20 can be reached. In contrast, polyolefins, such as polyethylene (PE) or polypropylene (PP), which have been processed in an extrusion blow-molding method, have a total stretching factor of mostly less than 5. Extrusion-blow-molded plastic containers therefore have lower mechanical strength values compared to stretch-blow-molded PET containers and for that reason are not internal-pressure-resistant for example. Carbon-dioxide-enriched liquids are therefore not stored in extrusion-blow-molded plastic containers.
For certain applications of PET containers, for example in the area of detergents, the containers can have necks with very large inside diameters, for example 30 mm to 150 mm. The use of special preforms, which can be produced in a plastic injection method, for example in an injection-molding method, can entail very high costs. This results from the fact that for the production of preforms with large opening diameters or neck widths, very high closing forces are involved to keep the injection tool closed.
For this purpose, either very large and expensive injection-molding machines are involved, or a number of smaller injection-molding machines with only a few injection cavities are used. The production costs for preforms with large opening diameters are therefore also high, since the opening diameters are generally not standardized. This means that for each new project, a new special preform is used, for whose production a new injection-molding mold is built.
In the production of preforms in an injection-molding method, the value of the wall thickness of the preform should not drop below, for example, 1 mm; in some units, the minimum wall thickness of the preform is even at least 2 mm. As a result, a large amount of material is used for example for the neck area of the preform. This increases the costs and results in an unnecessarily large use of material, which is also undesirable for ecological reasons.
Plastic containers with large opening diameters or large neck widths cause can however create issues for known stretch blow-molding methods. Standard stretch blow-molding devices have been designed for preforms with opening widths of 28 mm to 48 mm. For the processing of preforms with opening widths of more than 48 mm and greater, special stretch blow-molding devices are used.
To remedy these issues and to make possible a more economical production of plastic containers with large opening diameters, stretch-blow-molded plastic containers that have a cut neck have been established. Such plastic containers are produced from known preforms with standardized smaller opening diameters, as are used for the production of soft drink or water bottles, and the like. In the stretch blow-molding method, containers with a so-called dome, which is cut off from the respective plastic container after the stretch blow-molding process, are blow-molded from these known preforms.
The dome is located below the neck fixed for the preform in the injection-molding method. It has a considerably larger diameter than the preform neck and connects to the body of the container. The wide neck with the larger inside diameter is thus defined by the blow-molding process.
In this case, the outside contours, for example threaded sections or the like, are also defined on the neck of the plastic container that is later cut. This also allows the position of the outside threaded section or the same connection devices to be specified very precisely for the assembly of complex closure systems. The alignment tolerance for such special closure systems is often, for example, ±1° to ±3°. In the production method in the one- or two-stage stretch blow-molding method, the desired precision of the orientation of the threaded sections or such connection devices therefore can warrant use of a special heating technology of the preform and an exact orientation of the preform during insertion into the blow mold tool, which can further increase the effort for the production of the plastic container.
The quality of the cut neck, for example of the cut periphery, can be relatively poor. As a result, with stretch-blow-molded plastic containers with cut necks of the state of the art, an increased effort for the sealing of the neck opening should be taken into account. One way of sealing these containers, which can also have a can-like shape, and are equipped with lids, includes sealing inductively or conductively. This method can be expensive and involve relatively large investments in equipment.
Alternative sealing systems provide an arrangement in with a closure which is, for example, screwed on, with a soft closure insert made from an elastomer or from a foam material or the like. The sealing of the neck is then carried out by the pressing of the elastically deformable closure insert on the cut periphery of the cut neck. These additional closure inserts, however, can be incompatible with recycling specifications with respect to the use of raw materials that are as few and as uniform as possible, or they involve special, expensive separating steps during recycling.
From the state of the art, closure systems in which the irregularly cut periphery of the container neck is encompassed by a metal lid are also known. This closure variant can also be comparatively expensive, and not very desirable from the standpoint of recycling because of the different materials.